Three major research lines will be pursued: 1) Replication of globin genes during the cell cycle - It is proposed to determine the timing of globin genes replication during the cell cycle by using synchronized human cells. Techniques for obtaining DNA replicated during specific time intervals in the S phase will be used. The DNA thus obtained will be hybridized with labelled cDNA to human globin mRNA in order to establish if replication of globin genes occurs at a specific time during the cell cycle. Heteroploid HeLa cells and diploid human cell lines will be used. 2) As a model system we will study the replication of histone genes during the cell cycle. Similar techniques for synchronizing cells and for obtaining DNA replicated at specific times during the cell cycle will be used. In addition we will study the transcriptional and translational control of histone synthesis during the S phase. We will use analytical techniques to study directly the synthesis of histone mRNA and hybridization techniques with labelled histone mRNA or a copy of histone mRNA obtained with E. coli DNA polymerase to study histone mRNA synthesis in isolated nuclei. 3) The role of hemin in protein synthesis - We have recently observed that hemin added to the homogenizing medium of HeLa cells results in extracts highly active in initiation of protein synthesis. Previously, it has been almost impossible to obtain cell-free systems from these cells active in initiation of protein synthesis. It is thought that hemin stabilizes an initiation factor which is rapidly inactivated in its absence. We propose to study the mechanism of action of hemin in order to establish whether hemin has a specific role in protein synthesis.